A stereoscopic image display capable of selectively implementing a 2D image and a 3D image has been developed and has been put on the market due to the development of various contents and circuit technology. A method for implementing the 3D image of the stereoscopic image display is mainly classified into a stereoscopic technique and an auto-stereoscopic technique.
The stereoscopic technique, which uses a parallax image between left and right eyes of a user with a high stereoscopic effect, includes a glasses type method and a non-glasses type method, both of which have been put to practical use. In the non-glasses type method, an optical plate such as a parallax barrier for separating an optical axis of the parallax image between the left and right eyes is generally installed in front of or behind a display screen. In the glasses type method, left and right eye images each having a different polarization direction are displayed on a display panel, and a stereoscopic image is implemented using polarized glasses or liquid crystal (LC) shutter glasses.
A glasses-type stereoscopic image display having LC shutter glasses alternately displays a left eye image and a right eye image on a display element every one frame and opens and closes a left eye shutter and a right eye shutter of LC shutter glasses in synchronization with a display timing, thereby implementing the 3D image. In the glasses-type stereoscopic image display having the LC shutter glasses, because the LC shutter glasses have a short data-on time, a luminance of the 3D image is low. Further, a 3D crosstalk is extremely generated because of the synchronization between the display element and the LC shutter glasses and the On/Off conversion response characteristic.
In a polarized-glasses-type stereoscopic image display, a polarization separation device, such as a patterned retarder, has to be attached to a display panel. The patterned retarder separates polarized light of a left eye image and a right eye image displayed on the display panel. A viewer wears polarized glasses when viewing a stereoscopic image on the polarized-glasses-type stereoscopic image display. Hence, the viewer sees polarized light of the left eye image through a left eye filter of the polarized glasses and polarized light of the right eye image through a right eye filter of the polarized glasses, thereby giving a stereoscopic feeling.
The display panel of the existing polarized-glasses-type stereoscopic image display may use a liquid crystal display panel. A parallax is generated between a pixel array of the liquid crystal display panel and the patterned retarder due to a thickness of an upper glass substrate of the liquid crystal display panel and a thickness of an upper polarizing plate, and thus leads to a poor vertical viewing angle. When the viewer views a stereoscopic image displayed on the polarized-glasses-type stereoscopic image display at a vertical viewing angle higher or lower than the front of the liquid crystal display panel, he or she may feel the 3D crosstalk, where the left eye image and the right eye image overlap each other, when viewing the stereoscopic image with a single eye (i.e., the left eye or the right eye).
To solve the problem of the 3D crosstalk at the vertical viewing angle in the polarized-glasses-type stereoscopic image display, Japanese Laid Open Publication No. 2002-185983 proposed a method for forming black stripes on a patterned retarder (or 3D film) of a stereoscopic image display. In a method different from this method, the width of black matrices formed on a liquid crystal display panel can be increased. However, the formation of the black stripes on the patterned retarder may result in a reduction in luminance of 2D and 3D images, and the black matrices may interact with the black stripes, thereby generating moiré. Further, an increase in the width of the black matrices may reduce an aperture ratio, thereby reducing the luminance of the 2D and 3D images.
To solve the problem of the polarized glasses type stereoscopic image display disclosed in Japanese Laid Open Publication No. 2002-185983, Korean Patent Application No. 10-2009-0033534, filed on Apr. 17, 2009, and U.S. application Ser. No. 12/536,031, filed on Aug. 5, 2009, disclose a technology for dividing each of pixels of a display panel into two parts and controlling one of the two parts using an active black stripe. Korean Patent Application No. 10-2009-0033534 and U.S. application Ser. No. 12/536,031 are commonly assigned to the assignee of the present application, the contents of which are hereby incorporated herein by reference in their entirety. The stereoscopic image display proposed in the above-mentioned Korean and U.S. applications divides each of the pixels into the two parts and writes 2D image data to each of the divided pixels in a 2D mode to thereby prevent a reduction in a luminance of a 2D image, and also widens a vertical viewing angle of a 3D image. Hence, the stereoscopic image display proposed in the above-mentioned Korean and U.S. applications may improve the visibility of both the 2D and 3D images and may provide more excellent display quality than the existing stereoscopic image display. The active black stripe may include a thin film transistor (TFT) and a liquid crystal cell. However, in the active black stripe technology, the number of gate lines increased because of the division of each pixel into the two parts, and thus configuration of a gate driver became complicated.
Accordingly, Korean Patent Application No. 10-2010-0023888, filed on Mar. 17, 2010, proposed a technology for discharging a voltage of a liquid crystal cell of an active black stripe up to a voltage of a black gray level in a 3D mode. Korean Patent Application No. 10-2010-0023888 is commonly assigned to the assignee of the present application, the content of which is incorporated herein by reference in its entirety. In this technology, a discharge control voltage was applied to a TFT of the active black stripe so as to discharge the active black stripe in the 3D mode. The discharge control voltage may be commonly supplied to the TFTs of all the active black stripes through a control line. The discharge control voltage may vary depending on a position of the display panel due to a line resistance of the control line. In this instance, because the discharge control voltage applied to the TFT of the active black stripe at the position greatly affected by the line resistance was less than a desired value, it was difficult to completely represent the black gray level. To increase the completeness of the technology of the active black stripe in the 3D mode, it is necessary to compensate for the discharge control voltage, so that the active black stripes on the entire screen can completely represent the black gray level.